The invention relates to a device for the vulcanization of tire blanks, which has at least one heatable mold for receiving the tire blank and which has at least one controllable supply device for a heating medium, which is provided with at least one valve.
In the production of tires, a plurality of production steps is performed. In a first production step, extruded strips of an elastomeric material are usually joined together on a tire building drum to form a tire blank. This is often carried out using wire-type reinforcing inserts made of steel to enable “steel-belted tires” to be produced.
The tire blank is then transferred to a heating press and, in said press, is inserted into a heatable mold and typically subjected to an internal pressure. In general, it is possible both for the mold which receives the tire blank to be heatable and for there to be the possibility of introducing a heating medium into the tire blank in order to subject it during vulcanization to an internal pressure, which contributes to stabilization of the predetermined tire contour.
Various substances can be used as heating media. Steam, hot water or hot nitrogen are widely used. The heating medium is typically fed to the vulcanization process via pneumatically activated valves. In general, “monostable” valves are used. In particular, use is made of valves which are closed in a normal state or which are open in a normal state. Valves which are closed in a normal state are often used in the area where heating medium is supplied. Here, the control medium forces the valves to transfer to an open state against a spring force. In the event of an emergency shutdown and/or a failure of the control pressure, the valves are transferred to a closed state by the spring force. Valves which are open in a normal state are typically used in the outlet area. Here, the springs thus force the valves into the open position in the event of a pressure failure. This ensures that the pressurized space is vented to the environment and, as a result, is depressurized and thus safe.
The use of electrically controlled valves is likewise already known. However, these valves are often slow in respect of the switching times that can be achieved. Moreover, these valves are often not capable of achieving a predetermined normal state in an open or closed position.
Likewise disadvantageous is the fact that, where the valves have a relatively large nominal diameter, there is a risk of a reduction in the pressure of the heating medium. Finally, the actuating forces required are often also relatively large.
In a typical tire production process, a large number of tire heating presses is often operated in fabrication shops. In the case of pneumatically controlled valves, very complex pipe routing is required to supply the pressurized gases. In pneumatic devices of this kind, leaks and other problems with leaktightness often lead to total losses of up to about 80 percent of the compressed air used. Thus significantly more compressed air must be provided than is required for the actual control processes. As a result, relatively large and thus relatively expensive compressors are required, or the number of compressors must be increased at corresponding cost. Here, the costs relate not only to the equipment costs per se but likewise to operating costs.